112 THE FORMS OF WATER IN 



which was one reason for our crossing the glacier 

 opposite to the Montanvert. There are two convex 

 sweeps on the eastern side to one on the western side, 

 hence on tho whole the eastern side of the Mer de Glace 

 is most riven . 



§ 43. Moraine-ridges, Glacier Tables, and Sand Cones. 



282. When you and I first crossed the Mer de Glace 

 from Trelaporte to the Couvercle, we found that the 

 stripes of rocks and rubbish which constituted the 

 medial moraines were ridges raised above the genera] 

 level of the glacier to a height at some places of twenty 

 or thirty feet. On examining these ridges we found the 

 rubbish to be superficial, and that it rested upon a great 

 spine of ice which ran along the back of the glacier. 

 By what means has this ridge of ice been raised ? 



283. Most boys have read the story of Dr. Franklin's 

 placing bits of cloth of various colours upon snow on a 

 sunny day. The bits of cloth sank in the snow, the 

 dark ones most. 



284. Consider this experiment. The sun's rays first 

 of all fall upon the upper surface of the cloth and warm 

 it. The heat is then conducted through the cloth to 

 the under surface, and the under surface passes it on to 

 the snow, which is finally liquefied by the heat. It is 

 quite manifest that the quantity of snow melted will 

 altogether depend upon the amount of heat sent from 

 the upper to the under surface of the cloth. 



